Objectives Although the medical literature currently provides a growing number of isolated case reports of patients with clinically well-defined antiphospholipid syndrome (APS) and persistently negative antiphospholipid antibodies (aPL), there are no studies including a series of patients addressing the clinical features of this condition.
Methods The authors assessed clinical manifestations of APS in 154 patients: 87 patients with seropositive APS and 67 patients with thrombosis and/or pregnancy morbidity persistently negative for aPL and presenting with at least two additional non-criteria manifestations of APS (the so-called ‘seronegative APS’, SN-APS). Patients were interviewed at the time of recruitment, and a retrospective file review was carried out.
Results There were no significant differences in the frequency of thrombotic events or obstetric morbidity in patients with SN-APS versus patients with seropositive APS: deep vein thrombosis (31.4% vs 31.0%), pulmonary embolism (23.8% vs 28.7%), stroke (14.9% vs 17.2%), transient ischaemic attack (11.9% vs 10.3%), early spontaneous abortions (67.1% vs 52.1%), stillbirths (62.5% vs 59.4%), prematurity (28.1% vs 21.7%) or pre-eclampsia (28.1% vs 23.1%).
Conclusions Classic and SN-APS patients show similar clinical profiles. The results suggest that clinical management in patients with APS should not be based only on the presence of conventional aPL.
Statistics from Altmetric.com
In daily clinical practice, it is not unusual to find patients with clinical manifestations suggestive of antiphospholipid syndrome (APS) who are persistently negative for the routinely used assays to detect anticardiolipin antibodies (aCL), lupus anticoagulant (LA) and anti-β2-glycoprotein-1 (anti-β2-GP1) antibodies. Therefore, the term ‘seronegative APS’ (SN-APS) has been coined to include these patients with clinical features suggestive of APS who are persistently negative for antiphospholipid antibodies (aPL).1
In this report, we describe the clinical manifestations in a series of patients with SN-APS and compare their characteristics with a subset of patients, all fulfilling the Sydney clinical and laboratory criteria for definite APS.2
Patients and methods
Study population and clinical assessment
Between March and September 2010, 154 consecutive patients with a suspected diagnosis of APS, all attending the Louise Coote Lupus Unit at St. Thomas' Hospital (London), were enrolled after research ethics committee approval and written consent were obtained. Patients were interviewed at the time of recruitment, and a retrospective file review was carried out. Clinical data collection included demographic information, general and APS-specific clinical characteristics, non-APS acquired and inherited thrombotic risk factors, medications and APS profile (primary vs systemic lupus erythematosus (SLE)-associated APS). Thrombotic events and pregnancy morbidity history were recorded.
This study included 87 patients with seropositive APS (SP-APS) and 67 patients with SN-APS matched for sex and age: the former group fulfilled the Sydney classification criteria for APS, and the latter had major clinical manifestations of APS but tested negative for LA, aCL and anti-β2-GP1 at least twice on two separate occasions. In addition to the major clinical criteria (vascular thrombosis and/or pregnancy morbidity), the presence of at least two of the following non-criteria manifestations associated with APS were required: (1) livedo reticularis,2 (2) Raynaud's phenomenon, (3) migranous headache,3 (4) cognitive dysfunction,4 (5) seizures, (6) chorea, (7) multiple sclerosis-like illness,5 (8) brain MRI white matter lesions, (9) mitral valve disease, (10) aortic valve disease, (11) one or two spontaneous abortions <10 weeks and (12) thrombocytopaenia (<100,000/mm3). Patients with either a clinical evidence or history of vasculitis were excluded from the study.
To describe, in each group of patients, the number and type of clinical thrombotic events as well as pregnancy morbidity according to the clinical manifestations from the Sydney classification criteria for APS.
The presence of LA was investigated by screening tests (dilute partial thromboplastin time and dilute Russell viper venom time) and confirmed by mixture and confirmatory tests.6
IgG and IgM aCL were measured by a standardised ELISA.7 Samples showing more than 40 General Public Licence and/or MPL were regarded as positive for aCL.
In patients who tested negative for LA and aCL, anti-β2-GP1 (IgG and IgM isotypes expressed in GPL/ml or MPL/ml, respectively) was measured with a standardised ELISA.8 Values exceeding the 99th percentile of those found in healthy individuals were considered positive.
Antinuclear antibody was detected by immunofluorescence, and anti-dsDNA were analysed by Crithidia luciliae and Farr assay.
Statistical analysis was performed by the PASW software, describing percentages and mean values with SD (in brackets). When testing for differences between groups for qualitative variables, the χ2 or Fisher's exact tests were employed. Differences between means were analysed by the Student t test. A p value of <0.05 was considered statistically significant.
Clinical patients' characteristics are shown in table 1. Mean age at the first pregnancy or thrombotic event was similar in patients with SN-APS versus patients with SP-APS.
Table 2 shows the relationship between subgroups of APS and other immune diseases. Overall, connective tissue diseases were more frequently present in SP-APS when compared to SN-APS, with SLE being the most prevalent in this group (39% vs 16.4%, p<0.001).
Clinical manifestations of APS were not different in patients with SLE and SN-APS versus groups with SP-APS: venous thrombosis, 5 out of 11 patients (45.4%) versus 18 out of 34 patients (52.9%); arterial thrombosis, 4 out of 11 patients (36.3%) versus 13 out of 34 patients (38.2%) and pregnancy morbidity, 8 out of 10 patients (80%) versus 19 out of 26 patients (73%).
aPL profile in patients with SP-APS was as follows: aCL alone were positive in 35.6%, LA in 36.7% and both aPL tested positive in 27.7%. Only one (1.1%) out of 87 patients tested positive only for anti-β2-GP1. The mean number of aPL tests performed per patient was 3.4 (1.6) in SN-APS and 3.1 (1.7) in SP-APS (p=0.62).
Clinical manifestations of APS are shown in table 3. There were no significant differences in the prevalence of any clinical thrombotic events. Recurrences of vascular events were associated with warfarin withdrawal or with international normalised ratio values below the recommended target in 82.3% of patients with SN-APS and 87.5% of patients with SP-APS (p=0.43).
Pregnancies were recorded in 64 (96.9%) out of 66 women with SN-APS and in 69 (86.2%) out of 80 women with SP-APS (p=0.03), with a similar mean number of pregnancies in both groups: 5.0 (2.8) versus 4.4 (3.1), p=0.19. There were no differences in the number of live births in the overall population: 1.6 (1.1) versus 1.7 (1.4); however, the rate of live births/pregnancies (ie, successful pregnancies) was lower in women with SN-APS than in women with SP-APS (38.2% vs 50.2%, p=0.03). A history of obstetric complications following the Sydney criteria was documented in 55 (85.9%) out of 64 women with SN-APS who had ever been pregnant and in 54 (78.2%) out of 69 women from the group with SP-APS (p=0.26). When we considered women with one to two early spontaneous abortions, pregnancy morbidity was recorded in 60 (93.7%) out of 64 patients versus 57 (82.6%) out of 69 patients, respectively (p=0.06) (table 3). There were no statistical differences in the number of obstetric events, including early spontaneous abortions, fetal deaths, prematurity or pre-eclampsia, between women SN-APS versus women with SP-APS.
There were no differences in the risk factors for arterial and venous thrombosis in both groups. Full thrombophilia profile was available in 24 (35.8%) patients in SN-APS versus 18 (20.6%) patients in SP-APS (p=0.04). For those with venous thrombosis, hereditary thrombophilia profile was carried out in 59.2% from the group with SN-APS versus 27.5% from the group with SP-APS (p=0.01). Heterozygous factor V Leiden was found in two patients with SN-APS and in one patient with SP-APS. Heterozygous protein S deficiency was also found in one patient with SP-APS.
There were no differences in the percentage of patients on anticoagulation (warfarin or heparin) treatment between groups with SN-APS and groups with SP-APS: 59.6% versus 60.8%, respectively. In addition, there were no differences between both APS groups in terms of concomitant medications.
APS diagnosis relies predominantly on laboratory results, where the detection of aPL is mandatory. However, routine screening tests (aCL, anti-β2-GP1 and LA) might miss some cases of true SP-APS by failing to pick up cases with other antibodies directed against different phospholipids or protein cofactors, such as prothrombin, phosphatidylethanolamine, annexin V and vimentin/cardiolipin complex.9 Nevertheless, their main disadvantage is that there is no standardisation for such assays.10 In our study, only one out of 87 patients with SP-APS who tested negative for aCL and LA showed positivity for anti-β2-GP1 alone, which underlines the necessity for looking for other antibodies in an attempt to increase the diagnostic yield in APS.
The frequency of the main clinical features in our study is consistent with those described in patients from the Euro-Phospholipid Project group.11 Furthermore, we observed no differences in the rate of vascular events in both subsets of patients with APS, that is, clinical features were similar regardless of the presence of aPL. As previously described,12 13 more than one third of patients with deep vein thrombosis from our study in whom anticoagulation was stopped had recurrent thrombosis. Based on the similar prevalence of vascular event recurrences in both subsets of patients in our study, it opens the question of how to manage these patients when aPL become negative.
Although the rate of obstetric complications such as early spontaneous abortions, fetal death, premature delivery and pre-eclampsia were similar in both groups, we recorded a history of a lower rate of successful pregnancies in the group with SN-APS, the most reliable explanation being that obstetricians probably overlook APS as a possible cause of obstetric morbidity in these patients. Thus, after clinical diagnosis of SN-APS, our policy is to treat these women in the same way as the patients with full-blown APS/aPL were treated.
We found that patients with SP-APS showed a higher prevalence of SLE. Further studies are needed to characterise the extent to which SLE is more closely associated to SP-APS rather than SN-APS. Clinically, our results are consistent with previous studies addressing the comparison of the main features of primary and secondary APS, where there were no differences in the rate of venous thrombosis, arterial events or fetal loss.14
The inherited thrombophilias do not seem to substantially increase the risk of arterial thrombosis, and routine screening is not indicated in patients with venous thrombosis provoked by immobility, surgery and malignancy.15 We did not perform a routine screening of inherited thrombophilias in all patients, the main reason being that natural anticoagulant activities are decreased in acute thrombotic events and also during oral anticoagulant treatment. However, data were retrievable in approximately 60 per cent of our patients with SN-APS and with venous thrombosis.
In summary, our results should help clinicians bear in mind that the possibility of SN-APS can exist in patients with strong evocative clinical evidence of the disease and that appropriate treatment may prevent thrombosis from recurring and improve fetal and maternal outcome.
Mrs Lee Meng Choong (Research Nurse) and Mrs Veronica Murru (BSc), Lupus Research Unit (St Thomas' Hospital, London, UK).
Funding Supported by a grant from the Instituto de Salud Carlos III, Spain (BA09/90006). Maria Laura Bertolaccini is funded by the Louise Gergel Fellowship.
Competing interest None.
Patient consent Obtained.
Ethics approval Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.